1. Field of the Invention
This disclosure relates to fuel vapor treating apparatuses each having a leak detection system, in particular, to fuel vapor treating apparatuses capable of checking for leaks while an engine is not running, and methods for checking for leaks.
2. Description of the Related Art
A gas vehicle is generally provided with a fuel vapor treating apparatus for preventing fuel vapor from releasing into the atmosphere while preventing breakage of a fuel tank caused by pressure increase therein. In a case that the fuel vapor treating apparatus has a crack, seal leakage or the like, the fuel vapor leaks from the fuel vapor treating apparatus. However, a driver cannot directly recognize such leaks of the fuel vapor. In order to solve such problem, a leak detection system for detecting leakage of the fuel vapor from the fuel vapor treating apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2001-294052.
The fuel vapor treating apparatus disclosed in Japanese Laid-Open Patent Publication No. 2001-294052 is configured as an evapo-purge system where an adsorbent canister and an air intake pipe for an engine are connected with each other such that fuel vapor trapped in the adsorbent canister is purged to the engine due to negative pressure generated in the engine. In addition, the leak detection system has a valve capable of blocking communication between the fuel tank and the adsorbent canister such that the fuel vapor treating apparatus is divided into a first area including the fuel tank and a second area including the adsorbent canister, a first pressure sensor for measuring internal pressure of the first area and a second pressure sensor for measuring internal pressure of the second area. When an absolute value of differential pressure between the internal pressure of the first area (mainly, the fuel tank) and the atmospheric pressure is equal to or higher than a predetermined value, check for leaks form the first area (mainly, the fuel tank) is performed based on internal pressure behavior of the first area that is hermetically closed in a sealed manner by closing the valve. On the other hand, when the absolute value is lower than the predetermined value, negative pressure generated in the engine is applied to the whole fuel vapor treating apparatus including the adsorbent canister and the fuel tank and then check for leaks is performed.
Japanese Laid-Open Patent Publication No. 2002-235608 discloses a fuel vapor treating apparatus equipped with an aspirator for generating negative pressure by using a portion of fuel discharged from a fuel pump. In the fuel vapor treating apparatus, the aspirator is connected with the fuel pump via a pressure regulator configured to control fuel pressure, and the canister is connected with a decompression chamber of the aspirator. Thus, negative pressure generated by supplying surplus fuel from the pressure regulator to the aspirator acts on the adsorbent canister, so that the fuel vapor trapped in the adsorbent canister is recovered to the fuel tank via the aspirator. Accordingly, the fuel vapor treating apparatus is configured as purgeless evaporation system for recovering the fuel vapor from the adsorbent canister to the fuel tank and not purging the fuel vapor to an intake pipe for an engine.
With respect to the fuel vapor treating apparatus disclosed in Japanese Laid-Open Patent Publication No. 2001-294052, because the internal pressure of the first area is utilized for checking for leaks from the first area when the differential pressure between the internal pressure of the first area and the atmospheric pressure is within the predetermined range, the fuel vapor treating apparatus can efficiently carry out such check. On the other hand, the fuel vapor treating apparatus checks for leaks from the second area including the adsorbent canister by utilizing negative pressure generated in the engine. Thus, the fuel vapor treating apparatus cannot detect leakage from the second area while the engine is not running. Thus, there has been need for improved leak detection systems.